In the manufacture of internally threaded, tapered pipe collars such as are typically utilized in the petroleum industry for pipe or tubing strings that are suspended within petroleum producing wells, it is necessary that the pipe collars be of quite accurate manufacture. For example, the opposed internally tapered threads must be coaxial within very close tolerances in order that the pipe sections joined by the coupling will be coaxial and can be readily suspended within the well without interference with other pipe structures. It is also mandatory that the opposed internally tapered thread forms have a high degree of coincidence and registry one with the other. The taper, pitches and thread forms must be accurately maintained within very close tolerance limits because it is necessary that the threaded pipe joints form a positive, leak proof seal to prevent escape of gas or liquid petroleum products from the tubing string into other portions of the well being produced. Where such tubing or pipe is employed in conventional surface supported or buried service for pipeline operations, obviously, it is desirable that the threads of the couplings and pipe joints be machined with sufficient accuracy that positive leak free type joints will be developed simply by joining pipe sections by means of couplings.
The machining of pipe couplings is a highly competitive commercial operation and machine time, labor and material savings are given careful consideration. Moreover, the complexity and productivity of the machining operation itself can quite easily enhance or materially interfere with commercially acceptable manufacture of pipe collars.